#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, k; cin >> n >> k; --k;
  vector<int> a(n); REP(i, n) cin >> a[i];
  if (a[k] == 0) {
    cout << "0\n";
    return 0;
  }
  int l = k - 1, r = k + 1;
  while (l >= 0 && a[l] > 0) {
    if (a[l] == 1) {
      --l;
      break;
    }
    --l;
  }
  while (r < n && a[r] > 0) {
    if (a[r] == 1) {
      ++r;
      break;
    }
    ++r;
  }
  ll ans = 0;
  if (a[k] == 1) {
    ll L = 0, R = 0;
    FOR(i, l + 1, k + 1) L += a[i];
    FOR(i, k, r) R += a[i];
    ans = max(L, R);
  } else {
    FOR(i, l + 1, r) ans += a[i];
  }
  cout << ans << '\n';
  return 0;
}